In the bakery industry staling as perceived by the firming of the food product due to moisture loss has always been an issue. This is especially true in fried bakery product such as doughnuts. The moisture of the fried baked product will migrate from the high vapor pressure area (inside the product) to the low vapor pressure area (low moisture surface) until equilibrium in the vapor pressure and moisture is reached. As this process continues the inside portion of the product known as the crumb has a decrease in moisture content which contributes to the perceived staleness and hardening of the fried bakery product. Doughnuts contained in a storage box become firm and slightly mealy after 2 or 3 days. When a conventional icing is applied to a fried bakery product, these products, especially doughnuts, stale even more rapidly due to the rapid moisture migration from the crumb of the fried bakery product to the icing.
Freeze-thaw stability is another problem associated with iced bakery products. Food consumers are increasingly demanding high quality food products that are nevertheless convenient and simple to prepare. While freezing is a convenient method of storing high quality food items, products can undergo undesirable changes during frozen storage. Also, thawing of the product can lead to modifications of the product that are undesirable. In particular, frozen products, such as icings, with very high concentrations of sugar can undergo undesirable changes upon frozen storage and/or upon thawing. During thawing atmospheric water will condense onto the icing. Furthermore, icings with high sucrose concentrations tend to attract moisture, which can collect on the surface of the icing. This moisture build-up is termed weeping. Moisture absorption also adversely affects the integrity of the icing and ultimately can cause the icing to slide off.
U.S. Pat. No. 5,028,442 describes a method of providing an improved donut which comprises:                a) covering a donut with a substantially uniform coating, said coating comprises:                    1. 60-95 wt. % of an edible lipid having a melting point above 99° F.; and            2. an amount of aqueous soluble sugar-containing syrup and water or water alone added to ingredient (1) to produce a moisture content in the coating composition having a relative humidity from 73-75% as measured in a sealed air-tight box having a controlled starting headspace of 70° F./60% relative humidity environment of 100 grams of said coating spread evenly onto a surface of a pan recorded at five minute intervals until the substantially equilibrated relative humidity is obtained; and                        b) coating the product of (a) with a substantially uniform coating of icing.        
The coating composition controls moisture migration for e.g. chocolate coated donuts which remain soft in texture and of stable quality over extended periods of time.
U.S. Pat. No. 5,304,389 describes a non-hygroscopic icing composition comprising sugar, fat and an emulsifier as the main components, wherein 80% by weight or more of said sugar is particles passing through a 63 μm mesh size sieve and 50% by weight or more of said sugar is particles having a size of from 45 μm to 63 μm and the sugar content in the icing is 50% by weight or more. Sucrose, glucose, erythritol, lactose, palatinose, DFA III and maltose are mentioned as examples of sugars that can be used.
WO 01/19203 describes a reheating tolerant icing composition containing at least 20 wt. % water, at least 0.1 wt. % gelling agent, 1-30 wt. % of a high solubility sugar and at least 5 wt. % of a low solubility sugar, the low solubility sugar having a solubility in water of less than 40 wt. % at 20° C., wherein said composition contains no more than 35 wt. % sucrose. Lactose, isomalt, mannitol and erythritol are mentioned as examples of low solubility sugars.
US 2004/0131752 describes a melt-resistant fudge article which comprises:                a liquid fat;        a matrix of sugar crystals; and        an emulsifier component to facilitate formation of the liquid fat component into droplets of at least substantially uniform size.        
The sugar may include at least one of sucrose, glucose, fructose, lactose, lactulose, maltose, trehalose, invert sugar, corn syrup, honey, and the sugar alcohol includes at least one of sorbitol, mannitol, maltitol, xylitol, erythritol, lactitol, or a combination thereof.